This application claims priority of Japanese Patent Application Number 2003-57518, filed on Mar. 4, 2003.
1. Field of the Invention
The present invention relates to a radar apparatus equipped with an abnormality detection function and, more particularly to an FM-CW radar apparatus equipped with a function for detecting an abnormality in the noise floor level.
2. Description of the Related Art
An FM-CW radar radiates forward transmitted waves frequency-modulated by a modulating signal of a triangular waveform alternating cyclically between an upsweep section and a downsweep section, and produces a beat signal by mixing the waves reflected from a target with a portion of the transmitted waves. When the frequency of the beat signal in the downsweep section is denoted by fb(down) and the frequency of the beat signal in the upsweep section by fb(up), the beat frequency fr due to the distance to the target and the beat frequency fd due to the relative velocity of the target are respectively calculated as
fr=(fb(down)+fb(up))/2xe2x80x83xe2x80x83(1)
fd=(fb(down)xe2x88x92fb(up))/2xe2x80x83xe2x80x83(2)
From these, the distance R to the target and the relative velocity V of the target can be respectively calculated as
R=cxc2x7frxc2x7T/4xcex94Fxe2x80x83xe2x80x83(3)
V=cxc2x7fdxc2x7/2f0xe2x80x83xe2x80x83(4)
(where c is the velocity of light, T is the period of the triangular wave, xcex94F is the frequency modulation width (frequency shift width), and f0 is the center frequency.) Therefore, the values of fb(down) and fb(up) are determined from the peaks appearing in the beat signal spectrum in the frequency domain obtained by Fourier transforming the beat signal, and the distance and the relative velocity of the target are determined using the equations (1) to (4).
If there is an abnormality of noise floor level in the Fourier transform result of the beat signal, an erroneous peak detection may result. There is therefore a need to detect an abnormality of noise floor level.
It is accordingly an object of the present invention to provide a radar apparatus, equipped with a function for detecting an abnormality of noise floor level, at low cost.
A radar apparatus according to the present invention comprises: a measuring unit measuring a target distance and a relative velocity by analyzing a peak appearing in a Fourier transform result of a beat signal produced between a frequency-modulated transmit wave and a reflected wave thereof; a unit substantially stopping the frequency modulation of the transmit wave; and an abnormality detecting unit detecting an abnormality of noise floor level based on the Fourier transform result obtained while the frequency modulation is substantially stopped.